Corrosion preventing fairwater caps



Jan. 24, 1956 J. G. TAFT 2,732,021

CORROSION PREVENTING FAIRWATER CAPS Filed March 16, 1955 A K T L/ /5 \9 5 5 1 R H H INVENTOR.

JOHN G. 7,4 FT

4 r TOE/V6 v5 United States Patent John G. Taft, Brooklyn, N. Y., assignor to Godfrey Propeller Adjusting Corporation, Brooklyn, N. Y., a corporation of New York Application March 16, 1953, Serial No. 342,657

Claims. (Cl. 170-159) It is recognized that marine propellers of bronze, or rudders, and other such appurtenances, of similar metals, carried upon steel shafts or adjacent steel hulls, are subject to corrosion in salt water, and that this can be effectively prevented by so mounting a particular type of a oi-metal assembly upon or in closely adjacent relationship to the propeller or other part to be protected. Most usually it is the bronze propeller upon a steel shaft that requires protection, and such protection has been afforded by clamping upon the shaft, close -to the propeller, a split collar consisting essentially of a core of steel, iron, bronze or other material of approximately the same potential in the electromotive series as the shaft, but in any event not higher in such series than the propeller, and a shroud cast upon such core, of a metal such as zinc that is higher in such series. The core, being clamped in good electrical contact with the shaft, becomes with the shaft one terminal of an electrolytic cell, and the zinc becomes the other terminal, and in time is eaten away by corrosion rather than the bronze of the propeller, although it can be recast and restored. An example of such a collar is found in the Godfrey Patent No. 2,067,839, dated January 12, 1937.

Such collars constitute additions to the propeller and shaft assembly, and despite their recognized advantages have certain disadvantages. They are always mounted on the shaft ahead of the propeller. This means, for one thing, that the shaft must be exposed, aft of the stuffing box, to a sufiicient length to permit ready attachment of the bi-metal collar, and to that extent the unsupported outboard length of the shaft must be longer than if no such collar were used. Such collars, even though concentrated close to the shaft, are somewhat of an interruption to the smooth flow of water to and past the propeller, and they create a certain amount of drag.

By the present invention the use of such a collar is eliminated, and with its elimination the disadvantages mentioned can be avoided. Instead, the same protection against corrosion is afforded by a bi-metal fairwater cap, such as should be a normal part of a propeller and shaft assembly. The fairwater cap, whether or not of bimetallic form, must be thoroughly secured in place immediately aft of the propeller, and the necessity for so doing automatically insures the best possible electrical contact between the bronze or steel core of the bi-metal cap of this invention (or an element whereto that core is so closely secured as to constitute in electrical efiect a part of the core) and the shaft, or the propeller itself.

The possibility, in one of the forms of the invention illustrated herein, of mounting the core of the fairwater cap directly in contact with the propeller, and of making that core of the same metal as the propeller, insures that the propeller and core conjointly will constitute the cathode of the electrolytic cell, of which the zinc shroud is the anode, and that the formation of a secondary cell with the steel shaft and hull as the cathode and the bronze of the propeller as the anode, will be 2,732,021 Patented Jan. 24, 1956 very unlikely so long as an appreciable quantity of zinc remains.

Because the fairwater cap of this invention is aft of the propeller it does not disturb the smooth flow of water past the propeller, and by its streamline form it tends to improve the smoothness of that flow. Even when the zinc shroud is badly corroded, it produces far less disturbance to smooth flow of water aft of the propeller than would any collar, especially a similarly corroded collar, located ahead of the propeller. The outboard length of the propeller shaft may be the very minimum necessary to receive and properly mount the propeller, without any excess length for the reception of a collar.

It is a particular object of the present invention to provide such a corrosion-preventing fairwater cap which is formed in two principal parts, one of which parts, made normally of bronze, is intended as a support for the whole, and individually is formed for securement to and removal from the propeller and shaft assembly, and the other of which is made of two metals of different electropotential, including normally the corrodible zinc and a base of bronze, this composite assembly being secured to the first part of the assembly with the bronze portions in contact, and the whole so arranged that when the zinc is corroded away to an undesirable point the entire fairwater cap may be removed, its principal parts separated, and a new bi-metal part substituted for the old one by a relatively simple operation, whereupon the rejuvenated fairwater cap is reinstalled.

It is also an object to provide such an arrangement in which the means for mounting the composite part upon the base part are protected and inaccessible, and hence non-removable, so long as the fairwater cap as a whole is applied to the propeller and shaft assembly.

A still further object of the invention is to provide such a fairwater cap which may be formed purely and simply as an attachment, or which may, in an alternative form, constitute, also, the lock nut of the propeller and shaft assembly.

It is an object, also, to provide a fairwater cap of the general nature indicated which, in addition to being simple and relatively inexpensive, will be found rugged in use.

With such objects as the above in mind, and others as will appear hereinafter, the present invention comprises the novel fairwater cap as shown in the accompanying drawings, and as will be more fully described and claimed hereinafter.

Figure 1 is an axial sectional view through the propellet and shaft assembly and the fairwater cap applied thereto, in the preferred form of the fairwater cap.

Figure 2 is a view similar to Figure 1, showing an alternative form of the fairwater cap.

The propeller, usually of bronze, including the hub H and blades B, is secured upon the propeller shaft S in the normal manner. This propeller shaft terminates in a threaded portion at T and in a reduced tip R which is frequently pierced for the reception of a retaining cotter key K. The propeller is held upon the shaft by means of a securing nut N and a lock nut L, both threaded upon the threads T.

The supporting element for the fairwater cap is shown in Figure 1 at 5, and in this form consists of a generally cylindrically skirt 6 and an inwardly directed flange 7 at its rear end. To the rear of this supporting element is a core consisting of a base 9 and a rearwardly directed stud 10 which preferably has a large head 11 upon it. Cast about the stud l0 and held on by the head 11 is a corrodible zinc shroud 13, faired onto the exposed margin of the base 9. The base 9 is preferably of bronze, as may be also the supporting element 5, or at least the material of which the shroud 13 is made is higher in the electromotive series than the metal of which the base 9 and the supporting element are made, and the base and the supporting element should be of the same metal as one another, and the same as the propeller and shaft assembly, so that there will be no appreciable local electrolytic action between them.

it will be noted that the base 9 is flat so that it seats in full face engagement with the flange 7 of the supporting element, and these two are secured together by means such as the bronze screws which pass through the flange 7 into the base 9, with their heads engaging the flange so as to draw together the flange 7 and the base 9. The base will ordinarily be domed to receive the rearwardly projecting tip R of the propeller shaft.

The fairwater cap thus constructed can be mounted as a complete assembly upon the propeller and shaft assembly, and is removable only as an assembly. In the form of Figure l the nut N is externally threaded at its forward end, its reduced rear end having the wrenchcngaging surfaces, and the skirt 6 is interiorly threaded, as indicated at 3, complementally to threads cut on the specially formed nut N, and it is by this means that the fair-water cap is mounted upon the propeller and shaft assembly. When so mounted, it will be observed that the screws 15 are wholly enclosed and hence inaccessible for removal, and, moreover, are so aligned with and close to the lock nut L that they cannot be removed even accidentally, and so the unintentional removal of the separable assembly is impossible. Moreover, the metal of the supporting element 5 is pressed closely against the hub H of the propeller, so that there is afforded the closest possible electrical continuity between the propeller and the core 9.

in the arrangement of Figure 2 the nut N1 may be considered a standard type nut, with the usual wrenchengaging surfaces, but in this arrangement, instead of employing a lock nut L, the flange 70 of the supporting element 5 is lengthened and thickened, and formed with wrench-engaging surfaces, and the skirt 6 is correspondingly shortened, if need be, to prevent its forward end contacting the hub H, and the flange '79 is interiorly threaded as at 80, complementally to the threads T of the propeller shaft. In other respects the fairwater cap is substantially the same as that already described, and in particular the separable bi-metal assembly may be identical with the separable assembly in the other form, or interchangeable therewith. In this arrangement the flange "7Q threaded home against the propeller-securing nut N1 serves as a lock nut, and serves additionally as the supporting means for the fairwater cap as a whole. When parts are thus assembled the heads of the screws 35 are completely inaccessible and have no room whatsoever in which to back off.

t is the intention to supply separable assemblies consisting of the bronze base 9 and zinc shroud 13 which for any given size will fit any given supporting element 5. The supporting element 5 will be retained by the boat operator and the separable assembly will be attached thereto. Whenever the zinc has been corroded away to an undesirable extent, the owner will remove the separable assembly, first of course removing the entire fairwater cap to gain access to the screws 15, and then will replace the separable assembly which was in place by a fresh one; the old one will be returned for recasting with additional zinc. The operation of replacing a worn-out assembly with a new one is accomplished simply and in a few minutes, and the recasting of the zinc portion of the turned-in separable assembly can be accomplished at a central foundry.

} claim as my invention:

1. A fairwater cap for securement upon and rearwardly ofv a marine propeller and shaft assembly, including a supporting element formed of a given metal, means for supporting said element removably from and at the rear end of the propeller and shaft assembly, a separable bi-metal assembly formed as a whole to constitute a rearward fairwater continuation of said supporting element, and comprising a base of the same metal as the supporting element and positioned, when assembled, in contact therewith, and a shroud cast upon said base and formed of metal higher than such given metal in the electromotive series, and removable means normally holding said supporting element and said separable bi-metal assembly together, with the two like metals in contact.

2. A fairwater cap for securement upon and rearwardly of a marine propeller and shaft assembly, including a supporting element located at the forward end of the cap and formed of bronze and having means for supporting it removably from the shaft, a separable bi-metal assembly formed as a whole and located to constitute a rearward fairwater continuation of said supporting element, and comprising a forward bronze base and a rearward zinc shroud cast about said base, and bonze screws removably securing the bronze base to the bronze supporting element, and supporting said bi-metal assembly upon said supporting element.

3. A fairwater cap for a marine propeller shaft as in claim 2 wherein the supporting element includes a generally cylindrical forwardly directed skirt and an inwardly directed flange at the skirts rear end, and the base includes a generally circular portion contacting said flange, and wherein the screws are located for access from the interior of the skirt and extend in the axial direction through the flange and circular portion to hold them together.

4. A fairwater cap for a marine propeller shaft as in claim 2, wherein the base includes a generally circular portion contacting said supporting element, and a headed stud projecting rearwardly from the circular portion for retention of the zinc which is cast around it.

5. A fairwater cap as in claim 4, wherein the stud is domed rearwardly from the circular portion for reception of the end of the propeller shaft.

6. A fairwater cap for securement upon and to the rear of a marine propeller and shaft assembly, which assembly includes a propeller shaft and a propeller-securing nut, said cap comprising a supporting clement formed of bronze, the front portion of said supporting element operatively connected for supporting engagement with said propeller shaft and engaging said propeller-securing nut, said supporting element including a generally cylindrical skirt surrounding said nut, and a radially inwardly directed flange at the rear end of said supporting element, and a separable assembly formed as a whole to constitute a rearward fairwater continuation of said supporting element, comprising a bronze base the forward face whereof contacts said flange, and a rearwardly directed stud, and a rearmostzinc shroud cast about said stud and upon said base; and means for the securernent upon and removal from the supporting element of said separable assembly.

7. A fairwater cap as in claim 6, wherein the means for securement of the separable assembly upon the supporting element comprise axially directed screws joining the flange and the base, and having their heads located interiorly of the skirt, and therefore inaccessible for reioval so long as said supporting element remains in place p n th Pr pelle haft sembly- 8. A fairwater cap as in claim 6, wherein the propellersecuring nut is exteriorly threaded and the supporting element is interiorly threaded for interengagement therewith.

9. A fairwater cap as in claim 6, wherein the propeller shaft is extcriorly threaded and the supporting element is interiorly threaded for interengagement therewith as a lock nut upon the propeller shaft.

10. A fairwater cap comprising a base of a given metal, a shroud at least partially surrounding said base and of a metal higher than the bases metal in the electromotive series, a supporting element formed for secure ment upon and aft of a marine propeller and shaft assembly, and of a metal of like potential to the bases metal in the electromotive series, means for removably securing the base, with its shroud, upon the supporting element, the supporting element, base, and shroud being externally shaped to constitute a rearwardly streamlined fairwater cap when assembled together and secured upon the propeller and shaft assembly.

References Cited in the file of this patent UNITED STATES PATENTS Doremus June 28, 1932 Godfrey Jan. 12, 1937 Blanchard Aug. 6, 1946 Hermanny June 22, 1948 Benson Sept. 25, 1951 Coffing Oct. 14, 1952 

